Running in parallel courses; (of screw threads, etc.) winding helically in courses that run side by side.
Late 19th century; earliest use found in Peter Tait (1831–1901), physicist and mathematician. From German paradrom (J. B. Listing 1847, in Göttinger Studien (Math. u. Naturwissensch. Abhandl.) 1 851; from Hellenistic Greek παράδρομος running alongside from ancient Greek παρα- + δρόμος course; compare ancient Greek παράδρομα spaces for getting through gaps) + -ic.